1. Field of the Invention
The present invention relates to a liquid crystal panel and a liquid crystal display device and, more particularly, to a liquid crystal panel and a liquid crystal display panel capable of enhancing transmittance of liquid crystal and preventing a phenomenon in which a screen color changes.
2. Description of the Related Art
Cathode ray tubes (CRTs) have long taken the lead of the display markets, but currently, a liquid crystal display (LCD) device having the advantage of being lightweight and thin, consuming less power, and being driven at a low voltage, is replacing in the display markets. The LCD device, in which liquid crystal, fluidic organic molecules like a liquid, are regularly arranged like a crystal, displays an image by using qualities that the molecular array is changed by an external electric field.
An image displayed on liquid crystal is formed by a plurality of pixels uniformly divided on a screen, and here, each pixel has red, green, and blue colors. A principle of displaying an image by the LCD will be described with reference to the accompanying drawings.
FIG. 1 is a schematic sectional view of an edge type LCD.
A light emitting diode (LED) 5a is mounted on an inner wall face of an LED assembly 5. Although not shown, a plurality of LEDs 5a are arranged to be spaced apart in a lengthwise direction of a light receiving face of a light guide plate 15.
A quantum dot rail Q is formed to be spaced apart in a direction in which the LEDs 5a output light. Here, the quantum do rail Q refers to an aggregate of particular molecules that convert energy of a light wavelength output from the LEDs 5a into different light wavelength energy. When light of monochromatic wavelength is made incident to the quantum dot rail Q, since molecules for converting light into light of wavelength of blue, red, and green are arranged in the quantum dot rail Q, blue light, red light, and green light are converted and output. The three beams of light output from the quantum dot rail Q are mixed into white light and proceeds toward a light receiving face of the light guide plate 15.
The white light made incident to the light guide plate 15 is made incident to a panel 20 through an upper optical sheet along with light reflected from a reflective sheet 12.
Here, the LED assembly 15, the reflective sheet 12, and the light guide plate 15 constitute a backlight unit 10.
The light made incident to the panel 20 proceeds to a liquid crystal layer 45 through a lower polarizer 21a and a thin film transistor (TFT) substrate 30.
The white light, passing through the liquid crystal layer 45, proceeds to a color filter substrate 50, and is filtered as blue light, green light, and red light by the color filter layer (not shown) and output to an upper polarizer 21b. 
Here, the three beams of light has light transmittance that changes according to a voltage applied from the underlying TFT of the liquid crystal layer 45, thus displaying an image of various colors.
However, light of every wavelength is not transmitted 100% through the liquid crystal layer 45. Thus, light transmittance of liquid crystal layer 45 is designed in consideration of the overall transmittance efficiency of three beams of light (e.g., red light, green light, and blue light). In this case, the liquid crystal layer 45 should be designed by maximizing the transmittance efficiency of a particular wavelength, and here, as the particular wavelength, a green wavelength is generally selected.
Thus, the liquid crystal layer 45 is designed such that light transmittance of green wavelength is the highest, and this is the same as designing a value Δnd of the liquid crystal layer 45.
Δn indicates an index of refraction anisotropy, which is equal to the difference between a parallel index of refraction and vertical index of refraction and equal to the difference between an extraordinary refractive index and an ordinary refractive index. Here, d is the thickness of the liquid crystal layer 45. The product of Δn and d is Δnd, and in general, Δnd is when the transmittance of the green wavelength is the highest.
However, the loss of transmittance is greatly generated in light other than the green wavelength.
FIG. 2 is a graph showing transmittance of each wavelength of the visible light region on a screen display unit of the related art LCD device.
The green wavelength range from 495 to 570 nm. As shown in FIG. 2, the transmittance is highest at the green wavelength. However, the transmittance is reduced toward the blue wavelength and red wavelength. The transmittance of blue wavelength is reduced by about 20% and that of the red wavelength is reduced by about 15%.
Quality of resolution, among various qualities of the LCD device, is lowered as the quantity of light in a light guide panel is reduced. Thus, the reduction in the transmittance degrades quality of the LCD device.
Also, color of a screen image is changed according to a change in the thickness of the liquid crystal layer. This will be described in detail with reference to the drawings.
FIG. 3 is a graph showing transmittance of each wavelength in the visible light region on the screen display unit according to the thickness of the liquid crystal layer of the related art LCD device.
Because a process manufacturing LCDs is not performed identically every time, the thickness of the liquid crystal is slightly changed whenever a process is performed. G1 is a spectrum when a process is normally performed according to a design target. G2 is a spectrum when the liquid crystal layer is formed to be thinner than the design target. G3 is a spectrum when the liquid crystal layer is formed to be thicker than the design target.
Transmittance of blue wavelength of G2 is slightly upper than that of G1, and transmittance of yellow wavelength and red wavelength of G2 is slightly lower than that of G1. Thus, the state of G1 is the case in which the screen is white, so it can be noted that the state of G2 is the case in which the white screen is more bluish on the whole than the screen of G1.
Transmittance of yellow wavelength of G3 is slightly higher than that of G1, and transmittance of blue wavelength is slightly lower than that of G1. Thus, it can be noted that the state of G3 is that white screen is slightly more yellowish on the whole than the screen of G1.
Namely, the change in the thickness of the liquid crystal layer causes the change in color on the screen due to the transmittance dispersibility of the wavelengths.